Fluids: Density, Upthrust & Viscosity

Unit 1 includes the behaviour of objects moving through fluids (liquids and gases).

Pressure and upthrust

Pressure in a fluid at depth $h$ is $p = h\rho g$. A submerged or floating object experiences an upthrust equal to the weight of fluid displaced (Archimedes' principle): $$\text{upthrust} = \rho_{fluid}\, V g$$ An object floats when upthrust equals its weight.